Although the reserves of limonite are very rich, it is indeed a typical refractory iron ore, because it has the characteristics of poor sorting indicators and easy sliming. We classify the common beneficiation methods of limonite into two types, namely, single beneficiation process and combined beneficiation process, which will be introduced one by one.
The single beneficiation process of limonite mainly includes gravity separation process, magnetic separation process and flotation process (the flotation process includes positive flotation and reverse flotation).
The so-called gravity separation is to use gravity for separation, as the main separation method of limonite, and in most cases, it is used to treat coarse disseminated ore.
In order to further improve the quality grade, most limonite concentrators usually adopt the ore washing gravity separation process. First, they use the drum screen washer, trough washer, scrubber and other equipment to wash the ore, and then use heavy media, jigs and other gravity separation equipment to separate limonite and pseudohematite. The advantages of this limonite beneficiation method are simple gravity separation equipment, low cost, less power consumption, and the disadvantages are low recovery rate, high tailings grade, which is not conducive to the comprehensive recovery of resources.
Beneficiation equipment used in gravity concentration process: sieve drum washer, trough washer and jig.
Since limonite ore contains iron, they are all magnetic. The difference of iron content in limonite ore also causes the difference of their magnetism. This allows us to beneficiate limonite ore through the difference of magnetism. Generally, high intensity magnetic separation is used to separate limonite ore, but the recovery rate of this limonite ore dressing method for fine grade (- 20um iron mineral) is poor.
Beneficiation equipment used in magnetic separation process: magnetic drum, magnetic separator, etc.
The single flotation method has a good recovery effect on fine iron minerals, but the flotation effect is seriously affected due to the easy sliming of limonite, so it is very important to consider desliming or strengthening the dispersion of slime before flotation. The slime is difficult to adhere to the surface of bubbles due to its fine particle size, forming a separate mineralized foam layer that floats out and is easy to adhere to the surface of coarse particles. When gangue mud is attached to the surface of coarse limonite, its selectivity and floatability decrease significantly; The specific surface and surface energy (activity) of the slime are large. First, a large number of flotation reagents are adsorbed (consumed), resulting in a large amount of slurry oil agents and high viscosity, reducing the selectivity and floatability of easily floated ores; Second, the hydration ability is strong. Once the slime adheres to the bubble, the hydration film on the bubble surface is not easy to remove, which brings serious difficulties to concentrate concentration and filtration, leading to a decline in the recovery rate.
The flotation process of limonite can be either direct flotation or reverse flotation. Research and practice show that reverse flotation is more suitable for improving the quality and reducing impurities of limonite ore. In addition, due to the loose crystal and large specific surface area of limonite particles, it is easy to absorb and consume a large amount of reagents in the flotation process. Therefore, this limonite beneficiation method should adopt a multi-stage dosing and multi-stage separation flotation process. At the same time, the closed flotation process formed by the return of middlings will reduce the separation indicators, and the centralized return of middlings will have less impact on the separation indicators than the sequential return of middlings.
Beneficiation equipment used in flotation process: SF flotation machine, BF flotation machine, XCF flotation machine, etc.
In general, the beneficiation method of limonite can adopt gravity separation - high intensity magnetic separation to obtain good separation effect, that is, limonite ore is subject to ore washing, screening classification and desliming after fine crushing or rod mill grinding, coarse particle grade is subject to gravity separation to obtain concentrate, intermediate particle grade is subject to roller magnetic separator to obtain concentrate, and fine particle grade and slime are subject to high gradient magnetic separator to obtain concentrate.
In order to improve the recovery rate of iron metal, regrinding and re concentration can be considered for the gravity concentration middlings, which can significantly improve the iron grade of the concentrate. At the same time, because the iron minerals in the fines and slime are recovered, a higher recovery rate can be obtained.
Beneficiation equipment used in this process: rod mill, vibrating screen, classifier, roller magnetic separator, etc.
When the grinding fineness reaches a certain value, sodium carbonate and sodium silicate are added in the grinding process, so that the slurry can be well dispersed. In this way, the selective flocculation method can enable the selective flocculation of limonite. But sometimes the single flocculation method is still difficult to improve the grade of limonite concentrate because a large number of coarse gangue minerals cannot be removed. Therefore, the flotation method can be used on the basis of selective flocculation to obtain better separation indicators.
Beneficiation equipment used in this process: flotation machine, flocculant system.
For low-grade and fine-grained disseminated limonite ore, only fine grinding can obtain high-grade iron concentrate, while sliming will occur at the same time, resulting in low recovery rate. At this time, flocculation strong magnetic separation method can be used as the beneficiation method for low-grade and fine-grained disseminated limonite ore.
The practice shows that under the condition of similar iron concentrate grades, the iron recovery rate of the combined flocculation high intensity magnetic separation process is 10.97% - 15.73% higher than that of the direct magnetic separation process, and the separation effect is better. The fine iron mineral lost in the strong magnetic separation operation is recovered by increasing its apparent particle size through selective flocculation and receiving greater magnetic force. Therefore, the combined process of flocculation and high intensity magnetic separation can be adopted for fine grained limonite, but the process of slurry dispersion and selective flocculation and the separation conditions of high intensity magnetic separator (mainly the ore feeding mode and flushing water volume) need to be properly controlled.
Beneficiation equipment used in this process: magnetic drum, magnetic separator, flocculant system, etc.
The output structure of limonite ore is special, which is easy to be crushed and argillated during crushing and grinding, leading to difficulty in separation and recovery, and its gangue mineral composition is different greatly. In view of the particularity of limonite ore, the mineral composition types of main iron minerals and gangue minerals in limonite ore should be determined through beneficiation test, and the suitable beneficiation process of limonite should be formulated accordingly. Remember not to apply indiscriminately.
